fix subscript magic giving unresolved generic param type

fixes nim-lang#19737

compiler/semcall.nim

@@ -725,7 +725,8 @@ proc semResolvedCall(c: PContext, x: var TCandidate,
   result = x.call
   instGenericConvertersSons(c, result, x)
   result[0] = newSymNode(finalCallee, getCallLineInfo(result[0]))
-  result.typ = finalCallee.typ.returnType
+  if finalCallee.magic notin {mArrGet, mArrPut}:
+    result.typ = finalCallee.typ.returnType
   updateDefaultParams(result)
 
 proc canDeref(n: PNode): bool {.inline.} =

tests/overload/m19737.nim

@@ -0,0 +1,10 @@
+type
+  UInt128* = object
+    lo, hi: uint64
+
+func `<`*(x, y: UInt128): bool =
+  (x.hi < y.hi) or ((x.hi == y.hi) and (x.lo < y.lo))
+
+when not defined(works):
+  func `>`*(x, y: UInt128): bool =
+    (x.hi > y.hi) or ((x.hi == y.hi) and (x.lo > y.lo))

tests/overload/t19737.nim

@@ -0,0 +1,15 @@
+# issue #19737
+
+import ./m19737
+
+var m: seq[uint64]
+
+proc foo(x: bool) = discard
+
+proc test[T: uint64|uint32](s: var seq[T]) =
+  var tmp = newSeq[T](1)
+  s = newSeq[T](1)
+
+  foo s[0] > tmp[0]
+
+test(m)